Low-temperature laser photolysis of aromatic ketones. Transient absorption spectra in neat diethylaniline at 77 K

Abstract

Optical absorption and luminescence studies have confirmed that benzophenone, xanthone, and fluorenone in neat diethylaniline form molecular complexes with diethylaniline at 77 K. The transient spectra of these aromatic ketones in neat diethylaniline were measured by nanosecond laser photolysis at 77 K. For benzophenone and xanthone, the transient spectra observed for the molecular complexes are in good agreement with a sum of the spectra of the anion radical of each ketone and the cation radical of diethylaniline, indicating that these transients are attributed to the triplet states of the molecular complexes with a strong charge-transfer interaction. On the other hand, the molecular complex of fluorenone in neat diethylaniline at 77 K gives the transient spectrum almost identical with the triplet-triplet absorption spectrum of fluorenone in toluene. The charge-transfer interaction between fluorenone and diethylaniline in the triplet molecular complex is concluded to be very weak. The laser photolysis of anthracene and pyrene in neat diethylaniline at 77 K were also studied for comparison with aromatic ketones.